1. Field of the Invention
The present invention relates in general to a method for making alloy additions to an overlay weld pool, and in particular to an improved method for increasing a selected metal component composition of a clad layer.
2. Description of the Related Art
The weld overlay process is well-established and has been in commercial-use for many years. Several common welding processes used in weld overlaying include: submerged-arc, conventional or pulsed gas metal arc welding (GMAW), cold or hot wire gas tungsten arc welding (GTAW), shielded metal arc welding (SMAW), flux-core arc welding (FCAW), plasma transferred arc (PTA), laser welding, and electron beam welding. Typical applications include the cladding of tubes, pipes, flanges, and fittings with a corrosion-resistant layer. Additionally, the sealing and wear areas of valves and pumps may be clad for wear resistance.
In the weld overlaying process, generally an arc is established between an electrode and the surface of the metal substrate or workpiece. The arc is used to melt a consumable filler metal and a small amount of substrate to form a weld pool on the surface of the metal workpiece. In addition to conventional arc welding processes, laser or electron beam welding can be used to form a weld pool. The weld pool region is typically protected from oxidation by either using a gaseous shield or vacuum. In the process, the filler metal may also conduct the current to establish and maintain the welding arc (consumable electrode) or it may be separately fed (cold wire) into the arc or weld pool. The form of the filler metal can either be a wire, powder, or strip. The composition of the weld pool is a function of the composition of the filler metal and dilution by the metal component. The resultant corrosion or wear-resistant weld overlay clad layer is generally a function of the weld pool's composition.
Currently, single pass gas metal arc weld cladding uses a 22% to 24% chromium (Cr) weld filler metal and a low carbon steel substrate which results in a 17%-20% chromium deposit. While it is known that the use of multiple pass overlay alloy cladding, for example, U.S. Pat. No. 3,133,184 can be used to produce an increased chromium composition clad layer, the method requires the more costly multiple passes and is limited by the chromium composition of available weld filler metals.
Also, custom composition weld filler metals, for example, U.S. Pat. No. 2,299,483, can be used in producing high chromium content clad layers; however, these filler metals are variable in composition, expensive, and prone to contamination.
Thus, it is desirable to have a method which would increase a selected metal component composition of a clad layer in a single pass weld overlay and not be limited by the composition of suitable weld filler metals. Preferably, the method would use weld filler metals that are readily available, inexpensive, and not as susceptible to contamination. Additionally, clad layers can exhibit a greater selected metal component composition than the weld filler metal used when weld pool dilution is reduced.